Electromechanical relays of the type with which this invention is concerned include one or more pairs of movable contacts that can be selectively brought into engagement to complete an electrical circuit, or moved apart to open the circuit. When the relay contacts are either brought together or moved apart, and a potential difference exists across the contacts, arcing occurs. A variety of techniques have been employed in the past to minimize the amount of arcing, and/or compensate for the arcing, to provide a relay that continues to operate effectively.
When an arc occurs, it is common for material to be transferred from one relay contact to another, and in many cases, an actual weld, albeit a small one, is formed between the contacts. In normally open relays, for example, if a weld is formed between contacts when the contacts are closed, the weld may tend to hold the contacts closed when operating forces are removed, and this may prevent the relay from opening as desired. Typically, electromechanical relays include a solenoid for physically pulling the contacts together, and rely on a spring to force the contacts open when the solenoid is de-energized.
It is common to arrange relay contacts so that they engage and/or separate with a combination of relative movements, including opening and closing movements generally perpendicular to the surfaces of the contacts, and wiping movements generally transverse to the surfaces. The relative wiping movement of the contacts reduces the tendency for arcing to create welds during opening or closing, and therefore makes the relay more reliable.
Another requirement for electromechanical relays is that they provide a sufficient air gap to allow the relay to withstand the desired operating voltage when the contacts are open. While arbitrarily large single air gaps can be provided, it has been noted that larger effective air gaps can be created in a relay by utilizing a pair of fixed contacts in combination with a bus bar. As used herein, we refer to fixed contacts and movable contacts, but it is to be understood that all that is required is that one set of contacts be movable relative to the other. It may be that either or both of the contacts is actually movable or fixed, as circumstances require.
An electrical circuit to be controlled by the relay is connected to the fixed contacts. A pair of movable contacts is attached to a bus bar that is arranged to place the movable contacts into engagement with fixed contacts or to move in the opposite direction to disconnect movable contacts from the fixed contacts. The gaps between the fixed and movable contacts in a bus bar arrangement are in series, and therefore a given gap is effectively doubled in a bus bar arrangement, thus providing a more compact high voltage relay, compared with one having the entire air gap in a single pair of contacts.
Heretofore, in relays using a bus bar arrangement, substantially rigid, that is inflexible, bus bars have been employed to carry the movable contacts. The bus bar has typically been cantilevered at the end of an arm controlled by a solenoid to move the bus bar into engagement with the fixed contacts, to close the circuit. Wiping has been provided in a direction transverse to the major axis of the bus bar, that is the axis lying along a line extending between contacts. While this arrangement is effective, it is physically large and there is a need for a more compact construction.
It is an object of this invention to provide a compact high current relay that overcomes some of the problems associated with relays heretofore known.
It is another object of this invention to provide a compact high current relay having a bus bar carrying movable contacts that is sufficiently flexible to allow wiping at the contacts as the contacts are closed, without the need for complex mechanical arrangements.